1. Field of the Invention
The present invention relates to a liquid droplet ejection apparatus, and particularly to a liquid droplet ejection apparatus in which each of liquid droplet ejection heads having a plurality of ejection ports is provided with a resistive sensor for determining conditions inside the liquid droplet ejection heads.
2. Description of the Related Art
There has been known as a liquid droplet ejection apparatus an inkjet recording apparatus (inkjet printer) with an inkjet head (liquid droplet ejection head) having multiple nozzles (liquid droplet ejection ports) arranged therein, in which the inkjet head and a recording medium are relatively moved and ink (liquid droplet) is ejected from the nozzles, whereby an image is formed on the recording medium.
As an ejecting method in such an inkjet recording apparatus, there have been known various methods. A known example is a piezoelectric printing system in which a diaphragm configuring a part of a pressure chamber (ink compressing chamber) is deformed due to deformation of a piezoelectric element (piezoelectric ceramic), the volume of the pressure chamber is changed, the ink is introduced into the pressure chamber from an ink supply channel when the volume of the pressure chamber is increased, and the ink inside the pressure chamber is ejected from nozzles as liquid droplets when the volume of the pressure chamber is reduced. There is also known a thermal inkjet printing system in which ink is heated by means of a heater to generate bubbles, and the ink is ejected by the expansion energy created as the bubbles grow.
In an image forming apparatus having in ink ejection head, such as an inkjet recording apparatus, although the ink is ejected by means of the various ejecting methods described above by feeding ink to the ink ejection head from an ink tank storing ink via an ink supply channel, it is necessary to stably discharge the ink so that the ejected amount, ejection speed, ejection direction, and the shape (volume) of the ink is always predetermined.
However, during printing, nozzles of an ink ejection head are always filled with ink so that printing can be executed immediately when there is in instruction for printing. Since the ink is exposed to the air, the ink inside the nozzles dries out, whereby the ink viscosity increases, causing clogs in the nozzles. Moreover, the ink viscosity changes due to environmental changes such as change in temperature, whereby the ink ejection condition becomes unstable.
In the related art, a resistive pressure determining element or temperature determining element is mounted on each of the nozzles in the ink ejection head to determine a state of the ink ejection head, whereby viscosity change of the ink is estimated based on ink ejection determination of temperature determination to change the drive waveform of the ink ejection head.
For example, as a system specializing in controlling the drive waveform by determining temperature, there is known a system in which a thermal resistance element (temperature sensor) is installed in the vicinity of each ink pressure chamber corresponding to each nozzle so that the ink temperature can be determined securely in response to even any temperature distribution or precipitous temperature change, and also the drive waveform with corrected amount of the ink viscosity change caused by the temperature change, whereby each of the piezoelectric elements is optimally driven automatically in response to the changes in the ink viscosity (see Japanese Patent Application Publication No. 3-272854, for example). By incorporating the temperature determination element in the drive circuit, a relatively simple circuit configuration is realized.
Moreover, for example, there is known a system in which nozzles are formed in a pressure sensor to form a nozzle plate for liquid injection apparatus, in other words, a nozzle plate is used as a pressure sensor constituted by a silicon diaphragm, to determine ink injection or pressure inside the pressure chamber (see Japanese Patent Application Publication No. 57-53366, for example). Further, in Japanese Patent Application Publication No. 57-53366, there is no particular description of a bridge circuit, but it has a drawing where the sensor is arranged in a form of a bridge circuit.
Furthermore, there is known, for example, a system in which pressure (change in ink) inside the chamber is determined every predetermined pulse by a pressure sensor disposed in the pressure chamber, or by a pressure sensor which also uses a drive element, and ejection of an ink droplet is subjected to feedback control so that printing is performed in a state in which change (pressure change) due to the ink property or environmental changes (see Japanese Patent Application Publication No. 6-155733, for example).
However, in the description in Japanese Patent Application Publication No. 3-272854, it is necessary to install a sensor and a determination circuit for each nozzle, and the problem here is that a circuit load is heavy.
Further, Japanese Patent Application Publication No. 57-53366 describes that a plurality of nozzles are arranged on one sensor plate to form a multi-nozzle plate, but the problem here is that the bridge circuit is not utilized proactively, and that the configuration of the determination circuit cannot be minimized.
Furthermore, in Japanese Patent Application Publication No. 6-155733, a determination circuit is necessary for every nozzle, and the problem here is that a circuit load is heavy.